All animals experience tissue injury from toxins, pathogens and bodily trauma throughout their lives. Repair and renewal of damaged tissues is essential, but we know little about this process at the molecular level, and understanding it is critical for the development of regenerative medicine. One common mechanism of tissue repair relies upon activation of stem cells to produce new tissue lost during injury. I will investigate the mechanisms controlling stem-cell-driven organ regeneration in the planarian Schmidtea mediterranea, an animal with a remarkable capacity for regrowth and a highly accessible stem cell population. I will focus on the pharynx, which can be selectively amputated and completely regenerates within ten days. My first goal is to define the cellular response to amputation and regeneration using BrdU incorporation and cell cycle analysis. Microarray analysis of animals undergoing pharynx regeneration will identify genes that are differentially regulated during this process. To uncover additional genes required for pharynx regeneration, I will couple a large-scale RNA interference (RNAi) screen of planarian cDNAs with pharynx amputation. Morphological, functional and anatomical phenotypes of RNAi-fed animals will identify putative candidate genes. For candidate regeneration genes, I will determine expression patterns during regeneration and characterize the anatomical and cellular phenotypes caused by gene knockdown. I will also determine whether candidate genes act specifically to recognize the absence of a pharynx. Together, these experiments will identify the molecular pathways involved in the assembly of new organs in adult animals. Relevance The research in this proposal explores how stem cells in adult animals are able to regenerate an entire organ after its removal. The experiments focus on planarians, animals that can regenerate every organ and have extremely accessible stem cells. Because stem cells are often activated during human injuries, these studies will contribute to our understanding of regenerative medicine and stem cell biology.